In order to obtain desired measurement data, widely practiced is a method in which a plurality of measurement electronic device units each having a measurement detector connected thereto and thus having a measurement function are used, and a common control device (a controller, a personal computer, or the like) controls these units to collect and process the measurement results by the respective measurement electronic device units.
In order to measure, for example, the shape of a camshaft being an engine part of an automobile, it is necessary to measure displacements of respective cams provided in the camshaft at each rotation angle.
A conventional method for this is such that, as shown in FIG. 20, probes of detectors 111 to 114 connected to a plurality of measurement electronic device units 101 to 104 respectively are individually set in contact with cam surfaces of respective cams 121 to 124 of a camshaft 120, and the detectors 111 to 114 are fixed on a line parallel to and a predetermined distance apart from the axis of the camshaft 120.
The displacement measurement is performed in such a manner that a pulse signal generated every time the camshaft 120 rotates by a predetermined angle is inputted to a controller 150 from an encoder 140 attached to a motor 130 for rotating the camshaft 120 and measured values detected by the respective measurement electronic device units 101 to 104 are individually inputted to the controller 150, so that the controller 150 stores the measured values (position data) on the respective cams 121 to 124 obtained every time the camshaft 120 rotates by the predetermined rotation angle to examine changes thereof.
In this case, however, simultaneity is reduced due to time lag between the measurement electronic device units 101 to 104 and the controller 150 and due to time lag that is caused because the controller 150 sequentially reads the values measured by the measurement electronic device units 101 to 104, as is generally practiced.
A specialized circuit has to be provided in order to allow the controller 150 to simultaneously read the values measured by all the measurement electronic device units 101 to 104, which poses problems that the system becomes complicated and expensive.
Here, as another method, available is a method in which the controller 150 issues a temporary save command of measurement data to all the measurement electronic device units 101 to 104 to prevent the measurement data from changing, and thereafter reads the measurement data in sequence.
This method, however, has a problem that the rotation speed of the camshaft 120 is not allowed to be high and thus it is not possible to speed up the measurement time.
Further, for example, in confirming if the thickness of a rolled iron plate falls within a prescribed value range by measuring the thickness of the iron plate at predetermined time intervals, since it is difficult to set a reference value for the measurement, the thickness is generally measured in such a manner that two detectors facing each other are disposed to sandwich the iron plate, and the sum of the measured values of the two detectors is calculated.
In this case, because the iron plate is continuously rolled, the measured values incessantly change. Moreover, since the rolled iron plate moves up and down, each of the measured values of the two detectors, if individually seen, often presents a larger change than the change of the plate thickness.
Thus, when a measured object is moving, it is important that the measured values of the two detectors are simultaneously measure values, and if their measurements are not simultaneous, the measured values become more unreliable.
Thus, in obtaining a desired measurement result by performing an arithmetic operation on measured values by a plurality of detectors, for ensuring higher reliability of the measurement result, it is very important that the measurements by the plural detectors are simultaneous and there is no time lag therebetween.
However, in a system in which an external device such as a personal computer reads values measured by two measurement electronic device units to calculate the sum thereof, a read operation of the measured value is performed twice, and time lag therebetween deteriorates reliability of the measured values.
In another example where the inclinations of two pins standing on one iron plate in an assembly product are to be measured, two measuring instruments are used for one pin and a difference between measured values thereof is calculated. Therefore, two sets of the two measuring instruments are provided. The two sets are individually positioned through zero resetting or the like by a positioning jig serving as a master.
For automating this, a zero reset signal is inputted from an external device, and the external device is generally connected to each of all the electronic device units by individual wiring. This poses a problem that the wiring becomes complicated.
If another method is used in which the electronic device units are mechanically and electrically connected to one another and an input signal such as a zero reset signal is routed through the wiring among them, the wiring is simplified, but in the aforesaid example where the inclinations of the two pins are measured, simultaneous zero resetting of the two measuring instruments for one pin is required. On the other hand, as for zero resetting of the two sets of the measuring instruments, separate zero resetting offers higher operability. Therefore, it is desirable that a command for zero resetting can be given separately to each set of several measuring instruments.
In some cases, addition/subtraction is performed on measured values of two measuring instruments as in the aforesaid example where the thickness of the iron plate is to be measured and in the aforesaid example where the inclinations of the two pins are to be measured, and in some other cases where an average height of a plane or an average outside diameter of a disk-shaped part is to be obtained, addition/subtraction is performed on measured values of three or more measuring instruments, and division is further performed thereon. In still other cases where a measured value is magnified/reduced using a lever mechanism, multiplication is performed on one measured value.
These arithmetic operations are generally performed by an operator reading displayed measured values of individual measurement instruments or by an external device performing an arithmetic operation on individual measured values.
However, reading the measured values by an operator has not only a problem of complicating the work but also a problem of operation mistakes that the operator might make. The arithmetic operation by the external device results in a heavy load on the external device, and also results in poor operability especially in maintenance work since the operation result cannot be visually confirmed.